Equipment enclosures are typically employed to encase electronic and/or electrical components, such as circuit card assemblies, printed circuit boards, discrete electrical components, or other equipment. The equipment enclosures provide protection from the surrounding environment, such as water, dust, dirt, vibration, electrical interference, or other environmental hazards. Also, when electronic equipment is used in human-equipment environments, such as when a human operator must interact with the equipment, electrostatic discharge (ESD) events can occur. ESD events can include static electrical discharges between a human operator or handler of electronic equipment and the equipment itself, among other events. The ESD energy typically follows a path to an electrical ground from the ESD source, such as a finger, clothing, or the device itself.
With regard to touchscreens in human machine interface devices, two basic constructions are available when mounting a touchscreen in a bezel—front loading and rear loading. Rear loading allows the front surface of the touchscreen to be in contact with the rear of the bezel and the seal can be implemented using a conductive adhesive. This method of construction does not present any challenges to existing assembly techniques. It has the disadvantage of introducing a ledge or shelf surrounding the touchscreen that accumulates materials from the environment, and can allow bacteria growth in environments where organics are present in the atmosphere. Front loading provides a flat (coplanar) front surface that does not accumulate material from the environment.
Moreover, ESD events in some environments can lead to explosions (e.g., in industrial settings relating to oil, gas, pharmaceuticals and paints). Standards and safeguards applicable in some areas require safety features and/or characteristics for equipment operated in such environments. For example, in Europe, the Appareils destineś à être utilisés en Atmosphères Explosibles (ATEX) directive comprises two directives describing what equipment and work environment characteristics are allowed in an environment with an explosive atmosphere. ATEX requires that electrical equipment be designed to avoid danger of ignition due to electrostatic charges under normal conditions of use, maintenance and cleaning. This ATEX requirement is satisfied by covering non-metallic surfaces with a bonded durable conductive coating.
One aim of the ATEX directives is to permit sales and operation of ATEX-compliant apparatus and systems within the EU without requiring separate testing and other formalities for each jurisdiction. Generally the ATEX equipment and protective systems directive applies whenever equipment has its own ignition source, is intended for operation in a potentially explosive atmosphere, and operates under normal atmospheric conditions. Electrostatic discharge is recognized by the ATEX directives as an effective ignition source.